Okay some from what I have read in the past is that you can catch some of the original after the elite four, but the only thing I have been hearing about is the you can you catch in the white forest.
I'm a confused on this matter so forgive my ignorance; but my questions are:

1) Can you catch some of or a good bit of the Gen. I-IV Pokemon in both Black and White (excluding the White forest)

2) And, if so, what is the list of the ones you can catch (excluding white forest as well)

Disclaimer: I have tried searching this online, however the keywords never come up with the correct answer. Thank you :)